If you can get the valve off (VERY difficult, as it is held in by Loctite Red), it doesn't hurt to fill it with water and empty it (which helps get the smell out). Until the valve is off and it has been rinsed and dried on the inside (steam from water can be very nasty as well), even an "empty" propane tank isn't.
After that, getting an experienced welder to slice it open with a cutting torch, this will get one a decent watering trough for animals, or if cut open around the top and holes punched in the bottom (without affecting the bottom ring), this will result in a smallish (but still usable) fireplace.
